Abstract: In this study, the air resistance inside a tunnel is decomposed into the resistance of the train head and tail due to the pressure differential, friction resistance of the carriage, pressure differential resistance of the entire train, and resistance of the air gravity around the train along the train′s direction of travel. A research method for calculating the air resistance within a single-sided slope tunnel that considers the slope of the tunnel is established using the characteristic line of a one-dimensional compressible flow model with unsteady entropy. These aim to explore the effects of the tunnel length, slope, shape of the slope, train speed, and altitude on the average air resistance, maximum air resistance, tunnel average air resistance factor, and maximum air resistance factor when a train passes through a high-speed railway tunnel in plateau area. The findings are as follows. (1) The pattern of variation in air resistance in a sloped tunnel when a train passes through it is related to the pressure wave outside the train and the air resistance of the gravity component, and the air resistance increases or decreases under the action of compressive and expanding waves. When a train passes through a singlesided uphill/downhill tunnel, a tunnel with a herringbone slope, or straight tunnels having different tunnel lengths, the most unfavorable slope type and critical tunnel length based on average air resistance exist. The average air resistance over the length of a 10 km long, single-sided uphill tunnel is at its highest when a train is passing through it, reaching 47.05 kN. (2) When a train passes through a single-sided, uphill tunnel, the average air resistance and maximum air resistance increase as the slope of the tunnel and the speed of the train increase, and they decrease as the altitude increases. Additionally, when the average air resistance is fitted to the train speed, the average air resistance inside a single-sided, uphill/downhill tunnel when a train is passing through it is approximately proportional to the power of 1.92 and 2.14 of the speed, respectively.

Key words: plateau high-speed railway, extra-long tunnel, super-long tunnel, air resistance in tunnel, slope type, altitude, slope, one-dimensional flow model